Only now, with its final season in the can, is The Wiregetting recognition as a TV masterpiece. Its creator, David Simon, talks to Kate Holmquist.

Having grown up in Baltimore, where my mother, who taught in a black inner-city primary school, kept a mattress at the back of her room for her first-grade pupils to sleep on, and where she spent her own money buying them lunch, I've always had a personal interest in The Wire. It's different from any other drama series in that the central character is a city: Baltimore, Maryland, one of the most class-divided cities in the US.

And within this city, The Wire's characters are ordinary children, teenagers and adults coping with extreme situations and themes - poverty, neglect, the sex industry, the death of the working class, the drugs war, the farce of an education system, and the death of true journalism. These big themes are portrayed ambiguously, refusing the armchair voyeur the comfort of good and evil, heroes and villains. If there is a villain, it's never the drug-dealer or the prostitute-smuggler or the crooked cop - it's the system.

David Simon, creator of The Wire, is a former journalist who grew up in the suburbs of Washington DC. He moved to Baltimore after attending the University of Maryland, when he got a job on the beleaguered Baltimore Sun. At one time, the Sun was one of the great US newspapers, but declining advertising and the rise of the internet forced it to cut staff and compromise its journalistic integrity. That's Simon's view anyway, expressed as recently as last week in the Washington Post, though journalists have defended themselves, accusing him of "fire-ant" rage.

Simon may get angry, but he directs his rage well. Children who are educated in business and success by drug-dealers; working-class longshoremen who think they can get involved in smuggling without paying a moral price; teachers who care so much it breaks their hearts; city councillors who bow to corruption; policemen driven by personal ambition - these people aren't good or bad, they're just coping with a corrupt system. And US newspapers aren't reflecting this, he believes.

Not that Simon sees himself as a hero. If there's a hero, it's hubris, which, in the true sense of Greek drama, wins every time.

My mother's hubris? Believing she could make a difference. Like some of the more positive characters in The Wire, she found herself a pawn in quite a complex political game. When I tell Simon my mother's experience, his eyes widen and he says: "That's a story in itself." And that's what makes The Wire so compelling: Simon has always been interested in real stories.

Truly affecting drama is based on actual life as it is lived. Simon's passion, as a young reporter, was for "narrative journalism" that informed the reader about the system through true experiences. This point of view led him to research and write a book, Homicide: A Year on the Killing Streets, which later became the basis of the TV series, Homicide: Life on the Street. Simon followed that with The Corner: A Year in the Life of an Inner-City Neighborhood, which became an Emmy-award winning mini-series, The Corner. Everything he's done in TV since has been based on material from these books, he says.

IN DUBLIN LAST week to conduct a masterclass for Fás Screen Training Ireland, attended by 200 writers, he said that he couldn't tell anyone how to break into the business. He had the luck to be noticed by native Baltimore film-maker Barry Levinson (Diner and Rain Man, among other successful films), who helped to turn Homicide the book into a TV series. But, apart from luck, all a storyteller has to rely on are integrity and honesty, Simon believes.

"If you're going to create a drama based in Dublin, you use Dublin writers and Dublin actors. You don't do the Hollywood version of Dublin," he says.

With up to 60 performers in a single season, many of them real people playing themselves, The Wire has never relied on the star status of its actors for its appeal (although a few would keep you watching, such as Dublin-born Aidan Gillen, who has appeared at the Gate, and Dominic West, who went to Trinity College Dublin and plays Det Jimmy McNulty, the troubled Irishman). Each character is a classic archetype who exists for dramatic purposes, to drive the story along.

Simon's insistence on focusing on story, rather than character, can be challenging for the viewer, who is required to absorb thumbnail sketches of characters they might see once an episode, only to have the satisfaction of seeing these lives played out several episodes down the line.

The Wire has never got top ratings. HBO, makers of the ultimate in superficial chick TV, Desperate Housewives, bankrolled The Wire for as long as it took for the kudos to come in. Time magazine called the series one of the best TV dramas of all time, and it was widely praised elsewhere. But the average American TV viewer couldn't understand the Baltimore accents, couldn't follow the complex plot - which is like a visual novel and requires staying power - and never found a feel-good factor to keep them watching. Result: cancelled masterpiece. The Wire will end after the current season.

Some commentators have described Simon's wide range of characters and situations as Dickensian. Over coffee in the Merrion Hotel, he politely rejects the comparison. Balzac, Zola, these are his touchstones, although he insists he's not comparing himself to the great French novelists. Pretension irritates him.

It amuses him that, with the fifth and final season of The Wire written, filmed and finished in every sense, journalists are finally taking notice.

"Until now, we were never covered outside the entertainment pages," he says. Now, journalists in the US are writing profound soul-searching pieces about the importance of The Wire, retrospective praise which, in Simon's interpretation, is journalistic introspection at its worst.

In Ireland, you can see The Wire on TG4 on Monday nights after midnight, with the fifth season scheduled for later in the spring. You can download it, and perhaps find it in the shops in box sets. HMV is selling seasons two and three at half-price, but orders each season according to customer demand (it is promised that season four will be in the shops shortly).

Meanwhile, Simon has already moved on. He has completed a three-part mini-series based on Generation Kill, Evan Wright's telling chronicle of what it was really like for American soldiers in Iraq during the 2003 invasion. And his next project? With the writers' strike ongoing, development is impossible.

He manages to keep himself in the public eye though. His criticisms of the Baltimore Sun have been the subject of analysis in the New Yorker, the Columbia Journalism Review and Slate magazine, and on National Public Radio. Despite being a successful TV mogul, he has continued his guerrilla war against what he sees as the decline of US newspaper journalism and its squandering of a chance to be the media of the future.

"At the moment when the internet was about to arrive, most big-city newspapers - having survived the arrival of television and confident in their advertising base - were neither hungry, nor worried, nor ambitious," he says.

Meanwhile, Slate has described The Wire as "the best TV show ever broadcast in America . . . no other programme has done remotely what this one does, namely to portray the social, political, and economic life of an American city with the scope, observational precision and moral vision of great literature".

I ask Simon if he has redirected into drama the idealism he felt when he was inspired to become a journalist by the Washington Post's coverage of Watergate. He says not - The Wire is drama, not journalism.

That may be so, but where else would you discover what life is really like for students and teachers in an inner-city west Baltimore school? Where else would you see why the US "war on drugs" has failed? What newspaper would have the column inches and personnel resources to relate these narratives?

Simon's major criticism of US newspapers is their obsession with the Pulitzer Prize, devoting resources and bending the truth towards one emotive point of view in their attempts to land US print journalism's version of an Oscar. The challenge for any journalist, he believes, is to hold two points of view simultaneously in the coverage of an issue.

This is what makes The Wire different: it presents not just two points of view, but several in a single episode. It is stubbornly ambiguous, leaving viewers space to judge for themselves.

The series is so on-message that even Barack Obama has his favourite character: Omar, the Robin Hood thug who steals from drug-dealers and gives to the poor. Simon has heard this about Obama and dismisses it with a cynical shrug, as if to say "he would, wouldn't he?".

Simon fell in love with the west of Ireland 15 years ago and has spent a lot of time there ever since. Currently in his second marriage, to Baltimore novelist Laura Lippman, who was a reporter at the Baltimore Sun for 20 years, Simon maintains a close friendship with his first wife and they share custody of their 13-year-old son. When I ask the title of Lippman's second book, Simon searches his memory, then comes up with it: Another Thing to Fall.

"'Tell them he plugged his wife's novel," he says in parting, with that ambiguous mixture of cynicism and caring that seems to define him, and the ethos of The Wire.

The fourth season of The Wire is currently on TG4 late on Monday nights. The fifth season will follow immediately afterwards